This invention relates to a novel apparatus and method for measuring the vapor pressure (sometimes called partial pressure) of a material in a gaseous mixture. The apparatus is particularly useful, although not limited to, detecting the vapor pressure of water in air, the value of which may be used to ascertain the absolute humidity, specific humidity, dew point temperature, and the like.
With reference to meteorological observation and data gathering, there has been a need for an instrument allowing measurement of the vapor pressure of water in the atmosphere to aid in meteorological studies. For instance, evaluation of evaporation intensity of a body of water, prediction of cloud level, frost occurrence, and the like is predicted upon an accurate measurement of the vapor pressure of water in its gaseous phase.
As is known in the art, relative humidity, being a ratio, does not allow reckoning of the vapor pressure without knowledge of other factors. Previous methods of gaging the vapor pressure of a material have been difficult to use and expensive to manufacture. For example, the psychrometric apparatus presents difficulty in that it requires a continuous supply of the liquid phase of the metered material and diagrams, tables, or the like to evaluate the vapor pressure. The fogging-mirror type of instrument necessitates an electrical source of energy, as well as expensive electronic components.